Until now, many attempts have been made to produce an onset model of hepatitis by introducing a hepatitis C virus (hereinafter, referred to as "HCV") gene into a small animal such as mouse and expressing the introduced gene (C. Pasquinelli et al., Abstract book of 2nd international meeting on hepatitis C virus and related viruses (Jul. 31-Aug. 5, 1994 San Diego, USA); C. Pasquinelli et al., Abstract book of 3rd international meeting on hepatitis C virus and related viruses (Aug. 28-Sep. 3, 1995 Gold coast, Australia); Kazuhiko Koike et al., J. General Virology 76 pp.3031-3038 1995; and T.Kato, Arch Virol 141 pp.951-958 1996). However, unlike many other genes, the HCV gene was difficult to be integrated into a murine individual, and even if it was successfully integrated into the animal, production of an HCV protein did not take place in most cases. Furthermore, even in the extremely rare case where an HCV protein was produced in the animal, use as a hepatitis model was impossible since the protein was produced from the fetal period, thereby causing an immunological tolerance which resulted in no animal exhibiting typical hepatitis symptoms after birth.